Search Documents

By Pier-Lorenzo Solari, Philippe Moisy, Michel Schlegel, Stephane Pellet-Rostaing, Eric Mendes, David Bengio, Richard Husar, Thomas Dumas

Ionic liquids (ILs) are molten salts composed of an organic cation that are liquid below 100 °C. They demonstrate unique physico-chemical properties such as good conductivity, negligible vapor pressure and non-flammability. As a consequence, they are often regarded as green solvents and could become an alternative to the use of both high-temperature molten salts and volatile organic solvents in rare-earth elements processing and recycling. The diversity of interactions existing in an ionic liquid allows the solubilization of both polar and apolar compounds. Moreover, coordinating functions on their composing ions can lead to stabilization of some species. For instance, in non-aqueous media, europium exists in the (II) oxidation state which is not stable in aqueous solutions. Understanding the mechanism of Eu(III) electrochemical reduction to Eu(II) and the stabilization of Eu(II) species in IL media could be of major interest for the development of innovative recycling processes. Using transient electrochemistry and UV-Vis spectroscopy we could get valuable information on the redox behavior of the Eu(III)/(II) couple in the ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([EMIm][NTf2]). Reduction of Eu(III) to Eu(II) and stability of Eu(II) was also studied thanks to a XAS-spectroelectrochemistry set up used to follow in situ the evolution of the XANES spectrum around the L3 edge of Eu during electrolysis.

Mar 1, 2018

By Xiangwen Wang

Electrochemical measurements associated with the electrowinning of lead metal from concentrated brine (NaCI) - lead chloride (PbCI,) electrolytes at temperatures in the range 328 to 353°K (55 - 80°C) were conducted. The electrodeposition of lead metal onto a lead rotating-disk electrode may be described by the electrodic reaction: {PbCl 4 2 + 2e- = Pb° + 4Cl-} The deposition-overpotential requirements are low (approximately 41mV per decade of current density - Am+), with a corresponding high exchange current (approximately 0.018 A.cm2). The diffusion coefficient of the electroactive PbC142- species in a 3.5 NaCl electrolyte at 353°K was insensitive to the total PbCI, concentration (0.01 to 0.1M), and its value was found to be (1.21*0.1)~10-5 cm2Is with a temperature-sensitivity coefficient (E,/R) of approximately 1.98x103K-1 (328OK(T<353OK).

Jan 1, 1993

By Jennifer Mager, G. P. Martins, Dean Mussatti

"The role of lead, at low concentrations in high pH cyanide-electrolytes, on the dissolution behavior of gold, has been a topic of scientific and industrial concern for well over a century. The recent paper by Kondos et al [1] at CANMET (1995) this continuing interest and apparent importance. Nevertheless, the mechanism(s) by which this (and other heavy metal) component influences the electrodics of this electrochemical system has still not been unequivocally demonstrated. Instead, several plausible hypotheses, by pioneering researchers in this field, have been advanced and reiterated OVer the ensuing years. While it is generally accepted, based on equilibrium elctrode-potential calculations, that reduction (or co-reduction when oxygen is present in the electrolyte) of lead on the gold surface may occur due to cementation (contact reduction), the cemented lead has never been characterized. The work presented has reexamined the role of lead in this system, by delineating the species distribution of these system components and by interpreting the results of potentiodynamic studies in conjunction with SEM analyses of a gold electrode.1. INTRODUCTIONThe leaching of gold ores in cyanide electrolytes has been practiced for well over a 100 years. Research conducted on this topic has been primarily focused on the effects of operating parameters such as concentrations of oxygen and cyanide, and the pH of the electrolyte; or the leaching behavior of carbonaceous and sulfitic gold-bearing materials.Mechanisms by which pure gold is leached in alkaline cyanide media, with oxygen serving as the oxidant, have been subjected to continual examination and re-examination in the published technical literature during this century. Recently, it has been speculated that without the presence in the electrolyte of trace heavy metals, such as lead or mercury, that gold would not be leachable. Researchers who have tackled this topic, have either considered heavy metals to be a natural occurrence in these systems and ignored the role they may serve in the leaching process, or they have deliberately focussed on controlling their concentrations in the system to undetectable limits. As a result, conflicting findings have been reported for what would appear - depending on the details provided in these reports - to be identical systems."

Jan 1, 1997

By Yifei Zhang, Jianzhong Li, Wenhao Zhang

Eletrochemical behavior and corrosion properties of a Ti–6Al–4V alloy fabricated by selective laser melting in artificial seawater at temperature ranges from 20 to 40 °C were investigated using electrochemical techniques, including potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), and Mott-Schottky measurement, etc. Equivalent circuits were simulated to investigate alloy surface and analytic effects of temperature on interface of alloy and solution. The results showed that corrosion potential increased with temperature rise, and the EIS presented a single capacitive resistance characteristics. When the temperature reached 35 °C or above, passive current increased, while the passivation phenomenon was not obvious and corresponding radiating arc radius reduced, indicating that the resistance decreased, conductivity of surface passivation film improved, and corrosion performance improved. According to the Mott-Schottky curves, alloys exhibited n-type semiconductor characteristics. With increasing temperature, conductivity of passivation film enhanced, and alloy corrosion resistance decreased. At 40 °C, alloy possessed the worst corrosion resistance.

Mar 1, 2018

By Hojat Naderi

In this research assisted leaching of chalcopyrite using sodium peroxodisulfate was studied. Electrochemical techniques such as Tafel analysis and electrochemical impedance spectroscopy (EIS) were used to investigate the surface reactions of a chalcopyrite electrode in the presence and absence of Na2S2O8. According to the results, addition of sodium peroxodisulfate increases the current exchange of the corrosion process and prevents the formation of a passive layer on the surface of the electrode. EIS tests show the trans-passive dissolution of the passive layer on the chalcopyrite electrode in presence of Na2S2O8. Equivalent electrochemical circuits were modeled for Na2S2O8-free and -containing solutions and the model parameters were compared to determine the effect of S2O8 2− on chalcopyrite dissolution. Copper dissolution from pure chalcopyrite mineral and chalcopyrite concentrate was carried out using 15 g/L sulfuric acid solution with and without Na2S2O8. Simultaneous presence of 10 g/L ferric ion and 40 g/L peroxodisulfate salt results in about 40 and 18% of Cu extraction from chalcopyrite concentrate and pure chalcopyrite mineral, after 96 h, respectively.

By Kuniaki Murase, Tetsuji Hirato, Koji Nitta, Yasuhiro Awakura

"The redox behavior of copper species in an ""ammonium imide"" room temperature molten salt was examined in order to clarify the applicability of the salt to the electroplating media of various metals. Trimethyl-n-hexylammonium bis(trifluoromethanesulfonyl)- amide (TMHA-Tf2N), having an electrochemical window of 5.6 V (50 °C), and corresponding copper(II) salt were synthesized. In TMHA-Tf2N media monovalent copper ion, Cu(I), was stable and Cu metal was oxidized, or corroded, in the presence of Cu(II) species. Cathodic electrodeposition of copper metal and anodic dissolution of it were, thus, one-electron reaction and their current efficiencies were almost 100%.IntroductionElectrodeposition of metals from aqueous solutions is an important soft process for manufacturing thin-film materials, surface finishing, and extractive metallurgy. However, the electrodeposition of base metals, such as zinc, chromium, and nickel, from aqueous media inevitably accompanies hydrogen evolution, which lowers the cathodic current efficiency of metal deposition. Since the electrodeposition of aluminium, titanium, and rare earths from aqueous media is actually impossible due to their largely negative redox potentials, nonaqueous media such as aprotic organic solvent and high-temperature molten salts have been employed for the electrodeposition of these metals. Room temperature molten salts (RTMS),1, 2) or room temperature ionic liquids, have also been developed as a promising electrolytes for the electrodeposition of base metals. In this field, chloroaluminates of alkylpyridinium or alkylimidazolium cation have been well investigated for aluminium3) or alluminium-alloy4-5) electroplating media. On the other hand, in order to avoid high hygroscopicity arising from the use of aluminium chloride, attempts have been made to combine the alkylimidazolium cations with fluorine-containing hydrophobic anions, e.g. BF4-,6) CF3SO3- (TfO-),7) (CF3SO2)2N- (Tf2N-),8) and H(HF)n-ions,9) and investigated for electrodeposition media.'°) Recently, a new series of RTMS consisting of tetraalkylammonium cations and Tf2N- anion, sometimes abbreviated as TFSI- anion, was found independently by MacFarlane et al.11, 12) and Matsumoto et al. 13) This type of RTMS, which is commonly named ""ammoniumimide"" salt, has a wide electrochemical window of ca. 5 V and, thus, the RTMS seems to be suited for practical application as a solvent for the electrodeposition process. In this paper, we report the electrochemical behavior of copper species in an ammoniumimide RTMS, trimethyl-n-hexylammonium bis(trifluoromethanesulfonyl)amide (TMHA-Tf2N)."

Jan 1, 2000

By L. Diaz, J. Serp, L. Massot, P. Chamelot, M. Gibilaro

The discovery of NdFeB permanent magnets helps to perform technologies with reduced weight and gives them access to miniaturization. The industrial process of production of the Nd-Fe alloy by electrolysis used to manufacture NdFeB magnets consists in reducing Nd3+ ions dissolved in molten fluoride salts. The electrochemical behavior of neodymium is studied in LiCl-KCl and LiCl molten salt systems, examining reduction mechanisms, potential deposition, and faradaic yields.

Mar 1, 2017

By Zhong g. Shui-ping

A new type Pb-Ag (0.8wt%)-Bi (0~5.0wt %) alloy used as anode in electrowinning of zinc from sulphuric acid electrolytes was prepared. The electrochemical properties of this ternary lead alloys have been tested and compared with those of Pb-Ag (0.8wt %) anodes used in industry. Results show the anodic overpotential decreases with the increasing of Bi content in the alloys. When the content of Bi was 1.0 wt% and 5.0 wt%, the anodic overpotential is about 40?50 mV and 60?80 mV lower than that of Pb-Ag (0.8wt %) alloy, respectively. The formation of oxide layers on the surface of these alloys was traced by LSV methods and the composition of the anodic oxide layers was characterized by XRD and SEM analysis. The surface layer on the two type anodes examined is mainly composed of a?PbO2 and ß?PbO2. But different structure of the surface layer was observed, Pb-Ag (0.8wt%)-Bi (1.0wt %) has a more fine-grained structure as compared to Pb-Ag (0.8wt %). But the film on Pb-Ag (0.8wt%)-Bi (3.0wt %) alloy is rather friable, cracked and not tightly attached to the anode.

Jan 1, 2008

By Kenneth N. Han

Ammonia has been found to be an effective leaching reagent for gold, silver and platinum group metals in the presence of appropriate oxidants. Electrochemical and kinetic aspects of the dissolution of elemental gold in ammoniacal solutions have been investigated. The cathodic reaction of aurous di-ammine on the gold cathode has been investigated first. From this investigation, the standard electro-potential of the cathodic reaction .and hence. the Gibbs free energy of formation of the aurous di-ammine were established. The solubility of gold in ammoniacal solutions was also examined in relation to ammonia concentration, temperature and concentration of various oxidants. The anodic reaction of the gold disk in ammonia? in the presence? of various oxidants including oxygen, ozon, hypochlorite, hydrogen peroxide, cupric and cobaltic ammine, and iodine was also examined and the results have been discussed. Excellent dissolution yielding of gold and many other metals, typically better than 95% recovery in 1&apos;-2 &apos;hours of leaching at a temperature ranging 80°C to 190°C has been observed. Test results of the dissolution of gold from elemental state as well as other sources including sulfidic ores and scrap are presented.

Jan 1, 1998

By Xiaofei Guan, Adam C. Powell, Uday B. Pal, Srikanth Gopalan

This paper reports a solid oxide membrane (SOM) electrolysis experiment using an LSM– Inconel inert anode current collector for production of Mg and O2 at 1423K. The electrochemical performance of the SOM cell was evaluated by using various electrochemical techniques including electrochemical impedance spectroscopy, potentiodynamic scans, and potentiostatic electrolysis. The effects of Mg solubility in the flux on the current efficiency and the YSZ membrane stability during SOM electrolysis were discussed and examined through experiment and modeling. The electronic transference number of the flux were measured to assess the Mg dissolution in the flux during SOM electrolysis. A negative correlation between the electronic transference number of the flux and the current efficiency of the SOM electrolysis was observed.

Jan 1, 2014

By O. Forsén

A new cell construction was designed for the study of the electrochemical behaviour of additives in conditions that simulate real copper, electrorefining. The behaviour of gelatine and thiourea was studied by applying different electrochemical methods, i.e. polarization resistance and voltametric measurements. In this study, individual galvanostatic electrolysis experiments were carried out for 120 hours. The organic additives were introduced to the electrolyte at certain intervals and their concentration was varied in the range &om zero to four ppm. An optical microscope was applied for the examination of copper cathode deposit microstructures. The results show that gelatine has a polarizing effect on the deposition potential of copper whereas even small amounts of thiourea depolarize the electrodeposition of copper. The maximum inhibitor efficiency of gelatine was obtained at a gelatine concentration of slightly lower than two ppm. When both gelatine and thiourea were present in the electrolyte, the depolarizing effect of thiourea exceeded completely the polarizing effect of gelatine. If chloride ions were added to gelatine and thiourea containing electrolyte, the electrochemical behaviour of the system was altered drastically. Chloride ions resulted in the prevailing of polarization effect caused by gelatine while the depolarizing effect of thiourea disappeared in this system. The polarizing effect of gelatine increased until chloride ion concentration of 30 ppm was reached. Also, the above electrochemical phenomena could be detected in the optical examination of copper deposit microstructure.

Jan 1, 1995

By Akram Alfantzai, Farzad Mohammadi, Maysam Mohammadi

"Degradation of lead anodes has always been a major concern among the electrowinning industries. In this study, the effect of agitation of the zinc electrowinning solution on the integrity of lead anodes was investigated. Galvanostatic experiments were performed at 37±0.5°C using 0,600 and l000rpm magnetic stirring rates for 24 hours. The Pb02 layer formed on the anode surface was reduced to PbS04 (discharged). The discharge information was used to calculate the amount of Pb02 present on the surface. Weight loss measurements along with the discharge calculations revealed that the degradation rate of the lead anode increased as the solution was stirred more vigorously. Furthermore, the amount of remaining Pb02 on the surfaces was decreased as a function of solution velocity. Therefore, it may be concluded that, degradation rate oflead anodes is controlled by detachment of the corrosion products from the surface rather than by electrochemical reactions. IntroductionElectrowinning is one of the extraction stages of zinc, in which pure zinc is deposited from acidic solution after froth flotation, roasting and leaching processes. The anode electrode materials play important roles in the electrowinning process. Their electrocatalytical capacities determine the oxygen evolution overpotential, and consequently the cell potential and energy efficiency of the zinc electrodeposition [l]. Purity of the zinc deposited on the cathode is affected by the solubility and corrosion resistance of the anode materials. Using insoluble materials as anode in the electrowinning leads to the higher purity of the deposited metal on the cathode[2]. Lead (Pb) and its alloys have been used as the anode in the zinc electrowinning because of its special properties such as relatively low cost, low melting point, insolubility in solutions containing sulphuric acid and high conductivity in both states of metallic and oxidized [3, 4]. In zinc electrowinnig, zinc reduction occurs on the cathode (reaction 1) and the oxygen evolution reaction (OER) (reaction 2) is the main anodic reaction [5, 6]."

Jan 1, 2013

By Henrik Gudbrandsen, Geir Martin Haarberg, Ana Maria Martinez, Karen S. Osen, Sverre Rolseth

"The Several approaches were tried for developing an electrochemical route for producing high purity silicon from molten salts. K2SiF6 and metallurgical grade silicon were used as the source of silicon. Molten LiF-KF and pure KF with additions of K2SiF6 were used as electrolytes at temperatures from 550 - 900 oC. Silicon was cathodically deposited and anodically dissolved in the fluoride electrolytes. High electrorefining efficiency was obtained for many elements after electrolysis experiments at constant potential or constant current. The main challenge was to reduce the contents of boron and phosphorus. Another difficulty was to remove inclusions of solidified electrolyte. The lowest energy consumption was estimated to be ~ 3 kWh/kg Si, while the best current efficiency for Si deposition was found to be ~ 95 %.IntroductionSilicon is the most important material for photovoltaic power generation devices because of high feasible efficiency, low ecological impact and slow degradation. Development of a new and less expensive route for producing silicon of the desired quality is necessary in order to make solar cells competitive. Electrochemical routes may be an alternative possibility, and many laboratory studies have been reported over the past few decades. Most of the studies have been performed in molten salts, chloride or fluoride, at moderate temperatures so that solid silicon was deposited at the cathode. The production of high purity silicon has shown an annual increase of about 25 %, due to the increasing demand of solar grade silicon (SoG-Si). For future increased use of solar energy it is important to develop alternative, more energy efficient and cheaper processes for SoG-Si production compared to the Siemens process.Common silicon sources have been SiO2 and K2SiF6 for electrowinning and MG-Si in the case of electrorefining. A serious challenge is to find an oxygen evolving anode for electrolytes containing dissolved oxides. Especially at moderate to high temperatures and in molten fluoride electrolytes this is a difficult task.Many experimental results have been reported in molten chloride electrolytes. Nohira et al. [1-3] and Chen et al. [4] cathodically deposited silicon by electrodeoxidation of solid SiO2 in molten CaCl2 by potentiostatic electrolysis. An alternatice approach is to use electrorefining of low-cost metallurgical grade silicon (MGSi) to produce SOG-Si. In previous studies [5], an MG-Si anode was used, and silicon was successfully electrodeposited on a molybdenum wire in a CaCl2 based melt. It was found that the anode was strongly passivated due to the precipitation of silicon. Also, some deposits detached from the molybdenum wire because of the poor adherence to the cathode.Considering the Cu-Si alloy which has a good segregation effect for some impurities, and should not passivate, could be a good candidate anode for electrorefining. [6]."

Jan 1, 2014

By E. Fockedey

he destruction of free cyanide on a Co3O4 doped carbon felt was studied. The experiments were done with an eiectrochemical filter press cell on dilute alkaline solutions containing 250 mg/l NaCN. No chloride ions were added to the solutions. The cobalt oxide protects the felt against corrosion and has a catalytic effect on the degradation of the cyanide. This kind of electrode allows working with current density as high as 1200 Aim without any visible degradation of the felt. The most interesting results were obtained with a current density of 400 Aim&apos; at which the cyanide concentration can be lowered to 5 mg/l with a current efficiency of more than 70 % and a specific energy consumption of about 10 kWh/ kg CN.

Jan 1, 1998

By G. Lissens

In this work the electrochemical combustion of dissolved organic species in a single compartment cell containing a titanium mesh cathode and a boron doped diamond anode has been studied, The organic molecules involved were complexing agents such as EDTA (ethylenediaminetetraacetic acid) or NTA (nitrilotriacetic acid) used in metal plating shops and bright nickel plating bath additives, From batch experiments, it is shown that complete decomplexing of EDTA and NIA is feasible. Complete TOC (Total Organic Carbon) removal from solutions containing 0.01 M EDTA, 0.02 M NTA and bright nickel plating bath additives could also be achieved. Recycling experiments show that decomplexing of EDTA and NTA solutions can be obtained at an average electrical energy input of ~20kWh.kg-1 of complexing agent. Decomplexing rates of respectively 3.l3 mmol.Ah-1 for EDTA and NTA have been obtained, The Instantaneous Current Efficiency (ICE) was 71% for EDTA and 95% by NTA, Simultaneous recovery of Cu from a 0.01 M Cu-EDTA solution has also been evaluated. A solution (1.8 dm3) containing 0.01 M EDTA and 528 ppm of Cu was treated in a single compartment cell at a current density of 2 A.dm-2. 73% of the TOC could be removed and a final copper concentration of 8 ppm was obtained.

Jan 1, 2003

By I. Gaballah

The electrochemical behavior of a chalcopyrite concentrate having a high pyrite content was studied in HC1 by potentiodynamic, potentiostatic and galvanostatic experiments using a cell having separate anodic and cathodic compartments. Anodic oxidation of chalcopyrite particles was realized both by their contact with the cunent feeder and by reaction with ferric and cupric ions. An increase of current leads to a more selective dissolution of chalcopyrite. Surface passivation was observed after an electrolysis time related to the cell current. Cathodic reduction of chalcopyrite concentrate seems to be more promising. Almost complete conversion of chalcopyrite to a copper sulfide (Cui.8.S) is observed, whereas no reaction of the pyrite was detected. This confirms the possible selective dissolution of copper from the chalcopyrite concentrate. Copper sulfide obtained by cathodic reduction was leached using a cupric chloride solution.

Jan 1, 1994

By J. Brent Hiskey

Carefully prepared gold-bearing arsenopyrite samples from different geographical locations were leached in alkaline cyanide solutions using an electro-dissolution technique. Special precautions were taken to utilize monosized and thoroughly characterized samples. The rates of iron, arsenic, gold and silver dissolution were measured as a function of temperature under controlled conditions in sodium cyanide media.

Jan 1, 1989

By John Snowberger III, J. Brent Hiskey

The electrochemical dissolution of super alloys containing different amounts of rhenium was investigated. The initial part of the investigation focused on the anodic dissolution of rhenium from second-generation (3% Re) and third-generation (6% Re) nickel based alloys. Exploratory electrochemical tests were conducted to evaluate solution chemistries and to establish fundamental dissolution behavior of the alloys. These included rotating disc electrode (RDE) cyclic voltammetry, linear sweep voltammetry, and chronoamperometry tests. Electrolytes comprising sulfuric acid, hydrochloric acid, and ammonium sulfate were examined. Of these, a 0.1 M HCl solution proved to be extremely effective for electrochemical dissolution of samples of CMSX-4, CMSX-10, and SC-180 alloys. This paper discusses in detail the electrochemical behavior of these alloys.

Jan 1, 2014

By Laurence G. Dyer, David G. Dixon, John Rumball, Maziar Eghbalnia, Edouard Asselin

"Linear scan voltarnmetry was used to determine the reactions that occur during the cyanidation of petzite (Ag3AuTe2). Gold oxidation in petzite requires more oxidising conditions than are required for pure gold, it also does not achieve the same current (related to reaction rate). Tellurium oxidation occurs at a similar potential in water and cyanide, but as a component of petzite is impeded somewhat in water, likely due to the stability of the precious metals. Pre-treatment of petzite to oxidise tellurium in the absence of cyanide prior to gold recovery appears to be at least moderately successful.IntroductionWhile gold occurs most prevalently in its native form, many other gold bearing phases appear throughout natural systems [I]. Tellurides are a common group of such minerals, many of which also contain silver, often existing in association with native gold deposits. The six major gold-bearing tellurides are calaverite (AuTe2), sylvanite [(Au, Ag)2Te4], montbrayite [(AuSb)zTe3], krennerite [(Au1-x, Ag,)Te2], petzite (Ag3AuTe2) and muthmannite (AuAgTe2) [2]. While several other phases exist they are much more complex (i .e. buckhornite), which dilutes and confuses the influence of each specific component. Studies of gold tellurides have predominantly focussed on calaverite as it is the simplest and most common phase, however petzite, commonly found in Australia and North America, is the focus of this investigation.Gold processing via cyanidation has been operated for more than a century and is a highly effective hydrometallurgical treatment of native gold deposits. However, some gold alloys such as tellurides have proven to be somewhat less responsive under the same conditions. Several groups have shown that gold/silver tellurides are amenable to cyanidation, but are significantly more refractory than native gold [3]. Pre-oxidation steps have been tested to remove constituents that would consume cyanide such as sulfides. Such species are also linked to the precipitation of oxidised telluriwn, forming a passive layer, further inhibiting gold recovery [2]. It is uncertain to the definite reasons underpinning the refractory nature of precious metal tellurides in conventional cyanidation."

Jan 1, 2012

By Thomas J. Keefe, O&apos

The effects of cobalt, B-naphthol, glue and antimony on the polarization behavior of zinc sulfate electrolyte were investigated. It was found that B-naphthol was beneficial in reducing the detrimental effects of cobalt while antimony and excess glue were each harmful. Since the nu cl eat ion over potential was insensiti1ve to coba1t, other regions of the polarization curve were used to indicate electrolyte balance. The low? current density area occurring in the reverse or anodic sweep direction was? often an indicator when an ?unstable condition existed. The two parameters evaluated were the degree of inflection in the polarization curve in the low current density region during scanning and the rate of current rise observed when the sample was potentiostated at -0.781 Volts (SHE). Using this technique, a two-additive system was shown to be desirable to control cobalt and antimony containing electrolytes. The structure of the deposits was examined using scanning electron microscope techniques.

Jan 1, 1985